Nitrogen doping in acetylene bonded two dimensional carbon crystals: Ab-initio forecast of electrocatalytic activities vis-à-vis boron doping

Abstract

A systematic first-principles study is carried out over N doped graphyne (αGy, βGy, γGy, δGy, RGy and 6,6,12Gy) and Graphdiyne (Gdy) family in search of prototype light element based oxygen reduction reaction (ORR) electrocatalysts. Acetylinic linkage sites are identified to be the most preferable sites for N doping and all these localized defect centers are universally observed to be highly active epicenters for trapping molecular di-oxygen. Even though all the considered prototypes are found to prefer the four-electron pathway, monotonically exothermic reaction paths throughout the reaction cycle are observed only for N doped βGy, γGy, 6,6,12Gy and Gdy systems. N doped γGy system is found to have almost zero free energy difference between the third and fourth protonation step which rendered high overpotential to it. For N doped βGy, 6,6,12Gy and Gdy, the fourth protonation step is found to be the rate limiting step and their overpotentials are estimated to be 1.08 V, 0.98 V and 1.17 V respectively. ORR intermediates for the current N doped as well as prior reported B doped Gy/Gdy systems are found to follow a linear scaling relation akin to those reported for transition metal, N doped graphene etc. that facilitated isolation of a single descriptor which is used to compare their electrocatalytic activities. N and B doped configurations are found to occupy the strong and weak binding leg of the activity volcano respectively while the former is found to display superior electrocatalytic activity in terms of the onset potential.